Master Volumes, Post and Pre "Phase Invertor....

[ConcreteVampire]

What's the difference?

Beneficial for low/room volume toanz?

Also specific to application on Marshall SLX's? (Specifically moddong the second MAster so I can have both!)

Cameron has it specifically advertised as a benefit to an amp that alread has a master volume...

school me please!

 

[Sixtonoize]

The difference is that with a Post-Phase Inverter Master Volume (PPIMV), you're hitting the Phase inverter with the full guts of the preamp, which causes the PI itself to distort as well.
In a regular (pre-PI) amp, the phase inverter rarely distorts - only when the master is pretty high and the power tubes are close to clipping themselves.

Some people like PPIMVs, as it causes the amp to sound "more cranked" at lower volumes because the PI distortion adds a different flavor than straight preamp OD. The only amp that I've tried out with a PPIMV has been a Marshall Vintage Modern, and I thought that it didn't sound that great at low volumes. It is, after all, a Marshall...but when you get a Marshall cranking, I'm not sure that the location of the Master Volume in the circuit makes too much difference, as long as it's LOUD.

 

[stephen sawall]

I am also interested in what others well say on this subject with all amps.

 

[glpg80]

PPIMV allows for assymetric clipping of the incoming signal, as each side of the PI is biased slightly different to flip phase angles 180 degrees out of phase with one another so that they can be seperately amplified and re-assembled once again at the OT, where the energy is converted from a high impedance, high voltage load to a low impedance, high current load with somewhat low voltage (~74V at max volume on the secondary when impedance matched)

what this means in a tonal standpoint relates to an assymetric clipping of the original signal - think saturated un-complex gain structure simillar to a 5150.

PPIMV's sound best when the amplifier master volume is set no less than half, and the input volume is set high.

Pre PIMV's give a much less complex gain structure since the phase inverter itself is not being subjected to clipping on the lower/upper sidebands - therefore blues playing and more harmonically cleaner players will like the pre-PI master volume better - as volume will mix a more perfect blend of power tube distortion and phase inverter distortion both - which leans itself to a more open 3D sound.

gain guys will like the post master the best, even moreso when boosting is involved. but anyone who has experienced both will probably say they like the pre the best.

 

[Vrad]

PPIMV allows for assymetric clipping of the incoming signal, as each side of the PI is biased slightly different to flip phase angles 180 degrees out of phase with one another so that they can be seperately amplified and re-assembled once again at the OT, where the energy is converted from a high impedance, high voltage load to a low impedance, high current load with somewhat low voltage (~74V at max volume on the secondary when impedance matched)

what this means in a tonal standpoint relates to an assymetric clipping of the original signal - think saturated un-complex gain structure simillar to a 5150.

PPIMV's sound best when the amplifier master volume is set no less than half, and the input volume is set high.

Pre PIMV's give a much less complex gain structure since the phase inverter itself is not being subjected to clipping on the lower/upper sidebands - therefore blues playing and more harmonically cleaner players will like the pre-PI master volume better - as volume will mix a more perfect blend of power tube distortion and phase inverter distortion both - which leans itself to a more open 3D sound.

gain guys will like the post master the best, even moreso when boosting is involved. but anyone who has experienced both will probably say they like the pre the best.

I had a PPIMV on my Super Lead. Its now wired it up with Pre PIMV. I like the Pre PIMV better.

 

[stephen sawall]

PPIMV's sound best when the amplifier master volume is set no less than half, and the input volume is set high.

This has always been my experience.
Thanks for the explanation.

 

[ConcreteVampire]

Great anwers guys.


Riddle me this, I'm considering this for a 50 watt w Marshall SLX, with obviously it's switchable A-B masters.

It's got a half power switch, and I'm a "Loud Stage volume" but really nothing beyond that type player. Cranking and stage miking my VHT 50 CL for example is plent for me for the tone I want.

I'd like th SLX to run along the same thought tone wise, so would this "2 masters" Set up give me the lower volume toanz? I.e 25 watts, first master at 5 or more? (LIke I play the CL at home...)

thanks for the replies!

 

[farmerjohn]

How does a post phase inverter master impact the feedback loop / damping? Wouldn't it fiddle with forward gain & in effect reduce the effectiveness of feedback in the circuit?

I don't know if this would even be a noticeable effect, but I'm just wondering.

 

[glpg80]

How does a post phase inverter master impact the feedback loop / damping? Wouldn't it fiddle with forward gain & in effect reduce the effectiveness of feedback in the circuit?

I don't know if this would even be a noticeable effect, but I'm just wondering.

actually it would be more dependent on what tap on the secondary of the OT the negative feedback is set as, and the setting you have it set as.

the negative feedback loop would only be hindered if the PPIMV is set below 40%, at 50% and above it really does nothing to hinder negative feedback and actually gives slightly more control over it in controlled feedback instances due to the phase inverter stage being pushed into saturation. this will also lend to a less tight, more staurated feeling in the amplifier which will make it easier to play - but still stay strong.

you get the same effect with pre setups as volume increases, and theres no hindering of the negative feedback at certain levels when the master is below 50%, and it also does not matter what tap the feedback is operating from, and also does not matter how many cabinets you are using compared to the picky PPIMV.

 

[War Admiral]

Me and Vrad talked a little about the differences of the 2 and the effects of NF here...

viewtopic.php?f=3&t=66090&p=755483&hilit=PPIMV#p755483

 

[stephen sawall]

....the negative feedback loop would only be hindered if the PPIMV is set below 40%, at 50% and above it really does nothing to hinder negative feedback .....

Is this part of the reason they do not sound that great below half ? Myself I like them up 75% or more. In some amps they smooth out the sound compared to having the master volume bypassed.

 

[War Admiral]

How does a post phase inverter master impact the feedback loop / damping? Wouldn't it fiddle with forward gain & in effect reduce the effectiveness of feedback in the circuit?

I don't know if this would even be a noticeable effect, but I'm just wondering.

actually it would be more dependent on what tap on the secondary of the OT the negative feedback is set as, and the setting you have it set as.

the negative feedback loop would only be hindered if the PPIMV is set below 40%, at 50% and above it really does nothing to hinder negative feedback and actually gives slightly more control over it in controlled feedback instances due to the phase inverter stage being pushed into saturation. this will also lend to a less tight, more staurated feeling in the amplifier which will make it easier to play - but still stay strong.

you get the same effect with pre setups as volume increases, and theres no hindering of the negative feedback at certain levels when the master is below 50%, and it also does not matter what tap the feedback is operating from, and also does not matter how many cabinets you are using compared to the picky PPIMV.

You would have to go a little higher than 40% on the PPIMV for it to show less but it will still be there but less...thats the whole point of having a MV is to bring the volume down and at 50% or higher you're pretty damn loud! You are better off having a pre-MV and a boost pedal of some sort imo. Then you will have your negative feedback working which a Marshall amp circuit needs to work properly.

 

[glpg80]

How does a post phase inverter master impact the feedback loop / damping? Wouldn't it fiddle with forward gain & in effect reduce the effectiveness of feedback in the circuit?

I don't know if this would even be a noticeable effect, but I'm just wondering.

actually it would be more dependent on what tap on the secondary of the OT the negative feedback is set as, and the setting you have it set as.

the negative feedback loop would only be hindered if the PPIMV is set below 40%, at 50% and above it really does nothing to hinder negative feedback and actually gives slightly more control over it in controlled feedback instances due to the phase inverter stage being pushed into saturation. this will also lend to a less tight, more staurated feeling in the amplifier which will make it easier to play - but still stay strong.

you get the same effect with pre setups as volume increases, and theres no hindering of the negative feedback at certain levels when the master is below 50%, and it also does not matter what tap the feedback is operating from, and also does not matter how many cabinets you are using compared to the picky PPIMV.

You would have to go a little higher than 40% on the PPIMV for it to show less but it will still be there but less...thats the whole point of having a MV is to bring the volume down and at 50% or higher you're pretty damn loud! You are better off having a pre-MV and a boost pedal of some sort imo. Then you will have your negative feedback working which a Marshall amp circuit needs to work properly.

a little higher than 40% is 50%....

you can juice the front, have the amp gain volume low, and the master volume at 50%, and still be well below "loud"

then there are dummy loads for the appartment guys - whole different ballpark though.

and most of what i said about the post, is counter-reacted by the explanation of the pre PIMV - reread it once more at the bottom

 

[glpg80]

....the negative feedback loop would only be hindered if the PPIMV is set below 40%, at 50% and above it really does nothing to hinder negative feedback .....

Is this part of the reason they do not sound that great below half ? Myself I like them up 75% or more. In some amps they smooth out the sound compared to having the master volume bypassed.

basically yes, you are chopping the balls off of a marshall and making it something it is not.

its why most high gain amplifiers do their master volume controls before the phase inverter - you are not messing with LNF or GNF of the PI tube and OT secondaries.

 

[War Admiral]

I hear what you're saying but when I said ''a little'' I meant a lot because as soon as you put that PPIMV in the circuit, that is bring it down anywhere below 10 you will be cutting into the NF. The lower you put it the more you screw with the NF. The reason why people want the PPIMV is to keep the preamp volume up high to get the grind...if not imo once again you are better off with a preMV and a boost pedal...and still having the circuit working properly.

 

[ConcreteVampire]

Right... very in-depth answers. (Way more info than I got at HCAF when I posed the same question....)

SO "Electro-mechanically", not such a good idea for my application, (The SLX, for "Room loud" crankage). Or just on general principal as applied to how Marshalls work their Phase invertors.
I should be more concerned about having the pre-amp modded to push as much juice into the Pre-PPI master as possible.

Accurate?

 

[stephen sawall]

Or just use pedals to get that extra edge. With a modification you are stuck with the sound. Pedals you can change the sound any time. Nothing wrong with modifications if you find something you like.

 

[Telephant]

'77 Superbass with PPIMV on 2. It sounds different than a regular MV but at low volume w/ lots of gain I like it.

 

[stephen sawall]

'77 Superbass with PPIMV on 2. It sounds different than a regular MV but at low volume w/ lots of gain I like it.

You can tell it is not real loud. I think I can hear pick noise coming thru the mic. Sounded good to me.

 

[glpg80]

Right... very in-depth answers. (Way more info than I got at HCAF when I posed the same question....)

SO "Electro-mechanically", not such a good idea for my application, (The SLX, for "Room loud" crankage). Or just on general principal as applied to how Marshalls work their Phase invertors.
I should be more concerned about having the pre-amp modded to push as much juice into the Pre-PPI master as possible.

Accurate?

thats what 5150's, camerons, fortins, laney's, and every other company has done. so yeah, pretty accurate